Telephonic concentrator



April 11, 1961 L. J. LlBols ETAL TELEPHONIC coNcENTRAToR 8 Sheets-Sheet 1 Filed June 26, 1959 LOUIS J'- Libos 4 /Dyrc MLuca5 ATTORNEY April 11, 1961 l L J, LIBOIS E -rAL 2,979,571

TELEPHONIC CONCENTRATOR Filed June 26, 1959 8 Sheets-Sheet 2 I V "TI I I I I I /f I J I v I l 1 I Iv I I I A I I TI-r I` fZ. I I I i I I .I

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INI/F//TOES ATroE/vfy April 11, 1961 v L. J. Lnaols ErAL TELEPHONIC coNcENTRAToR 8 Sheets-Sheet 5 Filed June 26, 1959 Alava/MWA Sa-FLL ATTore/ve/ April 11, 1961 L.J.L.1Bo|s ETAL 2,979,571

TELEPHONIC CONCENTRATOR Filed June 26, 1959 8 Sheets-Sheet 4 ATTORNEY April 11, 1961 1 J. LlBols ETAL 2,979,571

TELEPHONIC coNoENTRAToR Filed June. 2e, 1959 4-ss sheets-sheet 5 /z 75 |/7 l; .f /f 4 i 'L L .1

INVENTORS Lol/[s J-Libozs HJ/ewe/MLl/cs A Braham A Saffiz ATroR/YEY April 11, 1961 1 ,.1. L lBois ET AL TELEPHONIC CONCENTRATOR 8 Sheets-Sheet 6 Filed June 26, 1959 I v l Abraham Saffiiz April 11, 1961 l.. J. L1Bo|s ETAL 2,979,571

TELEPHONIC CONCENTRATOR INVNTRS Louis J Lbos PcerreMLL/cas 8 Sheets-Sheet 8 Filed June 26, 1959 8 INvEn/Tos Louis L L( bois 4 Piena/Lucas ATTORNEY nited States Patent O i 72,919,511 TELEPHOMC CONCENTRATQR Louis .L Libois, Rue Georges Sand, Paris, France, and

Pierre M. Lucas`,"11 Rue Abbe Derry, 'Issy-les-Moulineaux, Erance" "1 'c Fnea June 26, 19.59, ser. Nq. 823,072; Claims priority, application France July 26, 1958 l s claims. (c1. 17a-1s) This invention relates to a telephone traffic concentrator operating in junctionwith a completelyh velectronicjcenceives from the concentrator the identification signalof this calling subscriberfand in the ca 'se of a called sub# scriber supplies to the concentrator the identifications'ignal of this called subscriber and in both cases'indicates the trunk line to be taken. Asy a result, during the connection which is generally effected by means 'of'a rectangular switchboard or matrix `of crosspoints, this switchboard is controlled both in the 'co-ordinate of the incorning subscribers lines and in theco-ordinate ofthe' loutgoing trunks, that is to say the crosspoint is marked on both its line and trunk terminals.

In the other concentrators of the prior art, known as independent connection concentratorsn '(sC, for example, the U.S. patent application Ser. No. 642,699 [now Patent No. 2,951,907'],led February l27, 1,957, in the names of Ch. Marzin, Chappey and the' second-named of the present applicants for a Telephone Concentrator), the subscribers lines can be connectedto the trunks on a random basis and identification of the chosen trunk occurs in a subsequentvstepl As a v'conlsequence, during the connection, the switchboard is operated only on its line terminals which is an advantage. 'l

The concentrator according to the invention is of the independent connection type. l' "l 'I'he transmission of the identification signal of a calling subscriber or of an engaged trunk line from the concentrator to the central station and the transmission 'of the identification signal of a called subscriber or off'a trunk line to be released from lthe central station to the concentrator can be effected by allotting time intervals to the connection or release of different subscribers, each interval being characteristic of Vone subscriber, in accord'- ance ,with the known principles of multiplex'communic'ation systems of the time modulation type. This solution requires the-presence in the con'centratorv andiri `th e central station of synchronised scanning' devices." The synchronism must be ensured by meansof synchronizing pulses of a particular waveform.

Each subscribers line and each trunk can also ybe characterized by a coded identification signal of thedigit series code type. The subscribers identification signal andthe identification signal of the connected trunk are transmitted from the concentrator to the central station in the case of an originating call. The identification signal of a terminating call or the .trunk identification signal of 'a trunk to be released are transmitted from the central station to the concentrator. i

The concentratoraccording to the invention lis of the FCC' ' Patented Apr. 11, 1961 coded connection kind and is therefore an independent connection concentator codedin accordance with a series dde-5, f A. d k ,Y

The concentrator according to the invention comprises, in known"manner,y circuits known as gate circuits, associatedwith 4each incomingsubscribers line, which enable tothe distinguished four states or possible service conditionsof 'the subscribers line: the subscribers line is in open loop condition an'dnot connected, closed loop condition and not" connected,- open loop conditionT and connected or closed loop condition and' connected. The first service condition'corresponds tothe subscribers handset being on'vthefho'ok in idle conditiom'the seco'nd service condition to the subscribers handset being rerno'vediawait ing operation; the Ithird service condition to a called subscriber before he'answers or to a calling subscriber during the diallingpulses or to a subscriber who has hung up his handset at the end of a call before the release of his line; and` thel fourth'service condition corresponds to a subscriber during speech communication. In addition, as is' also known, the concentrator comprises in association with each trunk line a circuit known asa trunk equipment circuit which enables the marking of the engagement of the trunk line which is effected by the yswitchboard, and-'the carrying out of the release. Finally/,also in kn'ownrna'nrier, asignal' of a' chracteristic'fretiuency known as the loop frequency signal is transmitted on thek trunk Vline whenit is ybusyand when the subscribers line is not 'in the closedloop condition (the called subscriber riot having removed hi'sfhandset, or the calling subscriber beinginthecouse of dialling, or'a subscriber having repl'aeed `his handset butthe `linenot being yet released). The 'o'ljectfof the present invention is to provide a concntrator whichietlects automaticallyand without en# ternal control the connection of any calling subscriber to an '-idle` undesignated `trurikfand 'transmits' to the central station switchingnetwork the identification signal of the calling subscriber and that of the engaged'trunk line, which effects, under thecontrol of the central station, Vthe r1`e`a`se"of a designated trunk from which ity receives l the identification signal.' As a consequencegth'e coding and decoding devices"which` make a given subscribenor a given 'trunk correspond to a given codeare devices which must have a double operation: to`transinit the identifica'- tio'n" signal of amarked calling subscriber whi`ch`they have "detected by scanning'or of a" trunkrline Vengaged at random, in whichv case` they operate in a free-running manner, or to receive'from ther central vStationen identi-y fication signal of a called subscriber orof 'a trunk' line to be released and to mark this called'subscriber in/'order to connect him or this trunk line in order to 'release it', in which case they function in a controlled manner.n

Theconcentrator according to the invention" utilises coding-decoding circuits which essentially'consist'of"a group or register of binary s calers or biestable triggers associated with a decoding matrix known as the decoderY or distributor, thewhole' having a first input called the scaler'input Which're'ceives recurrent triggering pulses for operation as a binary sealer, a plurality of outputs known as scanning or distribution outputsat which impulses appear in succession kwhenthe rregister'is operating a'sa binaryscaler and a plurality of inputs andoutputs known as test or control inputs and outputs, bymeans 'of'wliich the'state' of'each binary sealer or trigger'circuit can vrbe tested without modification, 'or controlledv either `to change the state'or to confirm it. `To simplify the description the word register will be used to indicate the'y unit includingn the Vregister proper and the associated decoding cir'- cuit.' More: exactly, when theregister operates as a sealer, the decoder produces pulses which appear sequentially at different scanning or ,distribution outputs. WhenV the operation asa'scaleris stopped; the application of pulses at the test or control inputs enables to be obtained from the test or control outputs pulses which are characteristic of the state of each trigger circuit'by testing it without iniiuencing its state, or to modify the state of each trigger circuit or to confirm it if no modilication is neces-v sary.

According to the invention, on the one hand the gate circuits of the subscribers are connected to the horizontal leads of a rectangular switchboard and the trunk equipments are connected to thevertical leads of this switchboard, and on the other hand each gate circuit is connected to the scanning or distribution outputs of a subscribers register and each trunk equipment is connected to the scanning or distribution outputs of a trunk register.

A control and test register has certain of its distribution outputs connected to the test or control inputs of the sub-A scribers register, other distribution outputs connected to the test or control inputs of the trunk register and iinally a last distribution output connected in parallel to the subscribers gates. The connections between the control and test register and the subscribers and trunk registers are made through coincidence circuits which receive either potentials representing the state of the trigger circuits (in the case of test operation), or identification pulses arriving from the central station (in the case of control operation).

The apparatus operates in the following manner: v In normal operation, the subscribers register operates as a scaler and seeks through its scanning outputs a calling line. When such a line is detected, it is immediately connected to a free trunk. The number of the calling subscriber is then registered in the subscribers register and the number of the connected trunk, transmitted to the trunk register by the trunk equipment of the connected trunk, is registered in this latter register. The operation of the subscribers register as a sealer then stops (the trunk register never operates as a sealer) and the control and test register starts to operate as a free-running scaler, that is to say under the control of a local generator. It tests the numbers stored in the two registers, that is to say it transmits pulses through the coincidence circuits associated with the trigger circuits of the registers which, on the other hand, receive from the said trigger circuits potentials which are characteristic of their states. As a result, according to the state of the trigger circuits of the subscribers and trunk registers, the control and test register transmits to the central station successive positive or negative pulses which constitute first the code identification signal of the calling subscriber and then the code identication signal of the connected trunk.l Once the code transmission terminates, normal operation of the concentrator is resumed.

If a called subscriber is to be connected, the code identification signal of this subscriber is transmitted from the central station and the control and test register starts to operate as a controlled sealer. It introduces the received code into the subscribers register through the control inputs of the latter. This register marks the gate circuit of the called subscriber and the control and test register, through its scanning output connected in parallel with all the subscribers gate circuits, transmits a pulse which causes the connection to be established with a free trunk line. The number of this trunk line is transmitted to the central station as in the case in which the connected subscriberwas calling. If it is desired to release a given trunk, the code identitication signal of this trunk is transmitted by the central station and the con-trol and test register starts to operate as a controlled scaler. The control and test register distinguishes the identification signal of a called subscriber to be connected from the identification signal of a trunk line to be released by means of a start pulse which precedes the code pulses and the polarity of which is different in the two cases. The control and test register in'- troduces the received identification signal into the trunk register through the control inputs of the latter. The trunk register transmits a pulse to the corresponding trunk equipment, which effects the release.

The system provided by the present invention can be extended to the case in which the internal matrix of crosspoints of the concentrator comprises two stages of crosspoints, by effecting a connection betweenrthe two stages. v The `invention will now be described in detail with reference to the accompanying drawings, in which:

Figure 1 represents a concentrator according to the invention in the form of a block diagram; y

Figure 2 represents the gate circuit of a subscriber;

Figure 3 represents the control and test register, the subscribers register and the trunk register, their control devices and the circuits which interconnect them or which are associated with them;

Figure 4 represents the subscribers register and the subscribers distributor;

Figure 5 shows the trunk register and the associated coder and decoder;

Figure 6 represents the trunk equipment;

Figure 7 shows the code identification signal transmitter situated in the concentrator and the code identification signal receiver situated in the central station;

l Figure 8 represents the code identification signal transmitter in the central station and the code identification signal receiver in the concentrator;

Figure 9 shows the code identification signal translator situated in the central station; and

Figure l0 represents a modified trunk equipment suitable for a concentrator having two stages of crosspoints.

Referring to Figure 1, the subscribers set 1 is connected, through the subscribers line S, to the subscribers gate circuit 2. The gate circuit 2 is connected to the rectangular switchboard or matrix 10 through a lead 11 which is a horizontal lead of this matrix. A trunk equipment 23` is connected to the vertical lead 12 of this matrix. The equipment 23 is itself connected, through a trunk 21, to an incoming line equipment situated in the central station. The switchboard 10 is constituted by a number of crosspoints which may in known manner consist of cold cathode gas-lled tubes, transistors, etc. These crosspoints are indicated by the reference numeral 13.

The subscribers register includes an actual register 7 and an associated decoder .8. The register includes a number of bi-stable trigger circuits sucient to ensure that the decoder or distributor v8 has at least as many scanning outputs as there are subscribers connected to the concentrator. In the example described, it has been assumed that there are six trigger circuits 71 to 76 in the register and as a result 64 scanning outputs numberedv 81 to 144 in the subscribers distributor. Each ofrthese scanning outputs is connected to the gate circuit of a subscriber, such as the gate circuit 2, by a lead such as 182. When the subscribers register operates as a sealer, it is controlled by a generator 16, and in this case pulses appear in succession at the terminals 81-144.

The trunk register includes an actual register 17, an associated coding circuit 15 and an associated decoding circuit 18. The register comprises a number of trigger circuits suliicient to ensure that the coder 15 and decoder 18 have at least as many outputs (inputs for the Coder) as there4 are trunks connected to the concentrator. In the example described, it has been assumed that there are four trigger circuits 171-174, in the register, and as a consequence there are `16 scanning outputs numbered 181-196 in the trunk decoder and 16 inputs numbered 151-166 in the trunk coder. puts 151-166 and each of the outputs 181-196, input and output of the same order, are connected to a trunk equipment 23 through leads such as the leads 253 and 283 respectively.

The control and test register comprises an actual reg- Each of the in-v circuit 204. The coincidence circuit 205 allows them to pass when the detector 203 indicates the looping of the subscribers line. The coincidence circuit 206 allows them to pass when they occur at the same time as a connection pulse coming from the control and test decoder by way of the lead 35 (i.e. in the case of the connection of a called subscriber) The coincidence circuit 207 collects the connection pulses coming either from the coincidence circuit 205 or from the coincidence circuit 206 and applies them to the connection amplifier 209 which gives them an amplitude sutiicient ito cause the operation of one of the crosspoints.

The coincidence circuit 208 allows to pass the loop frequency signal coming from the generator 212 when the line is connected (fall of potential at the terminals 202) and not looped (absence of D.C. potential at the output of the call detector 203). As a result the coincidence circuit 208 is operative to pass a signal in the following cases: the subscriber is a calling subscriber and is dialling; the subscriber is a called subscriber and is being rung and has not yet replied; the subscriber has replaced his handset at the end of the conversation and has not yet been released.

A trigger circuit 32, serving for the whole of the concentrator and intended to characterize the phases of transmisison'of an identification signal from the concentrator ,to the central station, is connected to -the output of the coincidence circuit 207 in parallel with the switching am- ,plier 209. This trigger circuit 32 is operated at each connection, both when the subscriber is a calling subscriber (in which case the identification signal of the calling subscriber and that of the connected trunk must be transmited lto the central station) and in the case of a called subscriber (inv which case the identification signal of the trunk only must be sent to the central station). The operation of this trigger circuit is effected by way of the common lead 211. lts return to idle condition is effected through the lead 47 when the test decoder is in position 1115.

The trigger circuit 32 serves to stop the scaler operation of the subscribers register 7 by reducing the potential of the lead 67 when this trigger circuit is brought into operation and to start the generator 5 of the control and test register 4 by removing a blocking potential by way of the coincidence circuit 65.

Figure l comprises three units composed of a register and an associated decoder: the control and test register 4 andthe control and test decoder 6, the subscribers register 7 and the subscribers distributor 8, the trunk register 17 and the trunk decoder 18. As has been stated, these units all operate in the same manner and are particularly described with reference to Figures 3, 4 and 5.

The control and test register and control and test decoder are shown in Figure 3.

The test register 4 includes four trigger circuits 41-44 which can store the digits -15 -in vbinary form. The test decoder 6 is a decoding matrix of known type which causes signals appearing at the outputs zo-115 to correspond with the different binary combinations of the trigger circuits 41-44.

In the case of a calling subscriber, the control and test register 4 is under the control of the generator 5. Pulses appear successively at the terminals arrow. Those pulses appearing at the terminals l1-a6 serve to test the condition of the trigger circuits 71-76 in the subscribers register 7. Considering, for example, the case of the terminal a1 associated with the trigger circuit 71 the pulse which appears at this terminal al is sent through the lead 51" if the trigger circuit 71 is in its rest condition and through the lead 51j* if the trigger circuit 71 is in its operated condition. If the trigger circuit '71 is in its rest condition, the gate circuit 49 of the and type is rendered conductive through the lead S0 and a pulse -is applied to the lead 51* through the diode 52. If the trigger circuit 71 is in its operated condition, the gate circuit 49 of the and type is rendered conductive through the iead 50' and a pulse is applied to the lead 51+ through the diode 52. Thus, a pulse is obtained on one lead or the other according to the state of the tested trigger circuit; the condition of the other trigger circuits 72-76 is tested in the same manner.

Those pulses which appear at the terminals zg-am serve to test the condition of the trigger circuits 171-174 in the trunk register 17. The gateI circuits 59 and 59 of the and type then play the part of the gate circuits 49 and 49; the conductors 60 and 60' take the part of the leads 50 and 50' and the diodes 62 and 62' take the place of the diodes 52 and 52'.

In the case of a called subscriber, the control and test register 4 is no longer under the control of the associated generator but is now under the control of the pulses arriving fom -the central station through the conductors 22 and 30. Pulses appear at the terminals L11-a6 and serve not to test the condition of the trigger circuits 71-76, but to set these trigger circuits. Simultaneously the identilication pulses of the called subscriber arrive either on the lead 31+ if they are positive or on the lead 31- if they are negative. If the first pulse following the start pulse, which is intended to operate the trigger circuit 71, is positive and if this trigger circuit is in its rest condition, the gate circuit 49 is opened, the gate circuit 9 is also opened through the lead 53 and the trigger circuit is operated through the lead 54. If with the pulse following the start pulse still positive the trigger circuit 71 is in its operated condition, the gate circuit 49 is closed as is also the gate circuit 9 and the condition of the trigger circuit 71 is thus confirmed. If the pulse following the start pulse is negative, the trigger circuit 71 being in its rest condition, the gate circuit 49 is closed as is also the gate circuit 9' and the condition of the trigger circuit 71 is thus confirmed. Finally if the pulse following the start pulse is negative, the trigger circuit 71 being in its operated condition, the gate circuit 49 is conductive as is the gate circuit 9 and the trigger circuit is set to its rest condition through the lead 54'.

When a trunk line is disconnected, the test register 4 is still under the control of pulses arriving from the central station by way of the leads 22 and 30. These pulses appear at the terminals ag-alz and they serve to set the trigger circuits 171-174. The coincidence or gate circuits `19 and 19 of the and type then take the place of the coincidence or gate circuits 9 and 9', the leads 63 4and 63' take the place of the leads 53 and 53 and the leads 64 and 64' take the place of the leads 54 and 54.

The trigger circuits 41-44 of the register 4 are arranged as a binary scaler without provision for inhibition of the counting function. The stepping of the scaler can be effected in two ways, either through the input 55 when the register is controlled by the generator 5 which is represented in Figure 3 as an a-stable self-oscillating trigger circuit, or by way of the input 56 through the pulse repeater 38. This repeater 38 is brought into operation when an identification pulse arrives by Way of one or other of the leads 30 connected to the positive and negative terminals of the receiver 28 through the coincidence circuit 37 of the or type.

The trigger circuit 33 serves to cause the subscribers register 7 to change from operation as a sealer to the inhibited condition, this inhibition being caused by the reception of an identication start pulse.

The trigger circuit 33 is operated through the gate circuit 39 of the and type when, with the generator 16 in operation, an identilication pulse is received by the receiver 28 and leaves the repeater 38 (only the start element is eliective).

The trigger circuit 33 is reset through the coincidence circuit 57 of the and type when, with the generator 16 in operation, the control and test decoder 6 is in position a7, that is to say when there vis a positive pulse Von the connection 35 leading tothe subscribers gate circuit 2V.

The trigger circuit 33 can also be set to its rest condition through the lead 47 coming .from the output 115 of the control and test decoder 6, which provides a pulse which sets to the rest condition not onlythe trigger circuit 33 but also the trigger circuit 32 and the trigger circuits 171-174 ofthe trunk register 177. The coincidence circuit 58 of the or type allows the following combination to be realized: trigger circuit 33 in its rest condition; or stage 42 of the test register 4 in 'its rest condition; or stage 43 of the testregister 4 in its rest condition; or stage 44 of the test register 4 in its rest condition; that is to say the opposite of the combination: trigger circuit 33 in operational condition and control and test decoder in position am or a15.

` coincidence circuit 58 of the or type. provides the above-mentioned combination of the trigger circuit 33 in rest condition and one of the stages 42, 43, 44 of the test register in rest condition, the generator is locked in its rest conditionwhen a positive potential istransmitted by the and coincidence circuit 6,5. The generator 5 operates when it is not locked by the and coincidence circuit 65, that is to say in the following cases: either the trigger circuit 32 is in operation; .or the combination of the trigger circuit 33 in operation and the control and test decoder 6 in position am or als is present.

When a negative start element is received by 'the receiver 28, the lead 31, the lead 46 and the and coincidence circuit 66, it enables the control and test register 4 to cover in one step the first eight positions. The trigger circuit 44 is in fact directly excited andthe control and test decoder marks directly the position a8 (see the disconnection of a trunk line).

Figure 4 represents the subscribers register 7 and the subscribers distributor 8.

The subscribers register 7 include sixv trigger `circuits 71-76. These trigger circuits can either operate as a binary Scaler under the control of the generator 16 which is represented in the form of an a-stable trigger circuit, or can be inhibited at their input to enable the test def coder 6 to control and test their condition or to set them in accordance with the received identification signal or c-an be inhibited at their output.

The input for the scaling function is the input 77. When'the trigger circuit 16 goes from its rest condition to its operated condition it produces a pulse which is differentiated by the unit consisting of the condenser 713 and the resistor 714. The diiferentiated pulse, which isV positive, is transmitted vthrough the diodes 715 and 716 to the two inputs of the trigger circuit 71. This pulse is effective only if the potential of the point 717 is suiiiciently high, that is to say if the two trigger circuits 32 and 33, from the outputs of which this potential if formed, are both in the rest condition (during scanning the calls of calling subscribers).

The arrangement between two successive trigger -circuits 71-76 of the subscribers register 7 is the same as between the trigger circuit 16 and the rst trigger circuit 71 of the register. All the points such as 717 are situated on a lead 67 the potential of which is iixed, by way 0f resistors 720 and 724, by the trigger circuits 32 and 33. If these trigger circuits are both in the rest condition the potential of 67 is high and the subscribers distributor scans the subscribers gate circuits. If at least one of the trigger circuits 32 and 33 is in the operated condition the value of the potential of the lead 67 is reduced to such an extent that the triggering pulses applied to the input 77 of the register are not eiiective. The input 77 is thus inhibited. The condition of the trigger circuits 71-76 can then be either tested bythe control `serves to drive the disconnection amplifier 27351.

and test decoder 6 by way of leads such as 50,-.-59. or set by way of leads such as 54-54,

The inhibition of thevsubscribers distributor 8 which is a decoder takes place in the following manner:

1f the trigger circuit 33 and the generator 16 are both in the rest condition, the lead 34 is raised toa high potential, through the resistors 718 and 719, by the two outputs of the said trigger circuit and generator, which are themselves at a high potential. All the diodes such as 711, 712,721, 722 connected on one side to the lead 34 and on the other to the vertical leads of the subscribers register 8 are blocked. The subscribers distributor ,distributes pulses at its output terminals 81 to If one or the other of the trigger circuit 33 and the generator 16 is in its operated condition, the potential of the lead 34 is negative and the outputs of the subscribers register are inhibited. All the pulses appearing at the output of the trigger circuits are in effect shortcircuited to the lead 34 by the diodes 711, 712, 721, 722 through which passes the current pulse.

Figure 5 shows the trunk register 17 associated with the trunk coder 15 and the trunk decoder 18.

As ,has been stated above, all the registers such as 4, 7 and 1,17. operate in the same way. In the case of the register 17, the inhibition is always effective except when the trigger circuit 32 is in is operated condition and the test decoder is in position 113. A positive potential is then applied to the inhibition lead 36 to block all the diodes 1711 1712, 1721, 1722 This corresponds to the disconnection pulse sent by the control and test decoder `in position au, to the trunk equipment 2 3 indica-ted by theV trunk decoder 18. g

When a line has just been connected, a connection control pulse arrives from the trunk equipment 23 on the lead 253. The said pulse passes through the diodes of the trunk coder 15 and operates one or more of the trigger circuits l1-71-174. The trunk register 17 thus records .the identification signal of the trunk line which has been connected.

Figure 6 shows the trunk equipment 23. This equip.- rnent is of known type but includes certain simplifications.

The lead 12 leaving the switchboard 10 is connected to one of the terminals of the Yprimary winding of a transformer 2,32 the other terminal of which is grounded through a capacitor 233. The trunk 21 is connected to the' terminals of the `secondary winding of this transformer.

The tiring of a crosspoint 13 of the switchboard 10 causes an increase in the potential of the point 234. This p oint is connected to a capacitor 235 and, by way of the resistor 2.36 Ito a point of fixed potential, and the pulse which results from the potential increase is differentiated -by the circuit comprising the resistor 236 and -to ground through the diode 2137 and the other is applied to the terminal 153 of the trunk coder through the lead 253.

The lead 283 from Vthe terminal 183 of the trunk decoder terminates at a iirst vtransistor amplifier 238 which. The positive disconnection pulse received by the transistor 238 is converted by the latter into a negative pulse and by the disconnection amplifier 231 into a positive pulse of 'the necessary amplitude -which is applied to the point 2 3-4 to cause breakdown or extinction of the crosspoint 13. The purpose of the diode 39 is to prevent the iinal transistor 230 of the amplifier 231 from being unblocked during the'period of conversation. During this period the potential of the point 234 is actually greater than the potential of the base -of the transistor 230, and without the presence of the diode 239, the speech channel would be shunted by the two transistors 230 and 230 rendered conductive. 'Y

aevaeri disconnection, to prevent the capacitor 233 from shunting a part of the disconnection signal. In the rest condition, the diode 240 is conductive and the diode 240' is non-conductive. certain voltage. At the instant of tiring of a crosspoint, the potential of the point 234 increases again. When this increase in potential reaches a certain value, the diode 240 is rendered conductive and the diode 240 rendered non-conductive because the charge on the capacitor 233 cannot change instantaneously. The potential of the point 234 stabilises at a certain value; then the capacitor 233 charges progressively and, at the end of a certain period (4 milliseconds for example) the diodes 240 and 240' are both rendered conductive for speech currents or currents of loop frequency.

Figure 7 illustrates the identification signal sending device 29 on the concentrator side and the identification signal receiving device 928 on the central station side, and Figure 8 illustrates the identification signal sending device 929 on the central station side and the identification signal receiving device 28 on the concentrator side.

It should be noted that the pulses arriving by way of leads 51+ and 51- are of the same polarity and that those arriving by way of the lead 51+ must provide in the signalling line 20 positive signals, represented by the direction of the arrow 201, and that those arriving by way of the lead 51" must provide in the same line 20 negative signals, represented by the direction of the arrow 202. In a similar manner, positive signals represented by currents in the direction of the arrow 201 in the signalling line 22 (Figure 8) must provide pulses of a given polarity in lead 31+, and negative signals represented by currents in the direction of the arrow 202 in the same' line 22 must provide pulses of the same polarity in the lead 31,

The lead 51+ is connected to the base of a transistor 291 which controls two other transistors 293 and 295 of opposite kinds. When these two latter transistors become conductive, the potential of point 297 is increased and that of point 298 decreased. A positive current, in the direction of the arrow 201, is transmitted in the vsignalling line 20.

The lead 51+ is connected to the base of a transistor 292 which controls two other transistors 294 and 296 of opposite kinds. When these two latter transistors become conductive, the potential of the point 297 decreases and that of the point 298 increases. A negative current, in the direction of the arrow 202, is sent along the signalling line 20.

In the identication signal receiver 28 (Figure 8), the reference 281 indicates a transistor which ampliiies the positive signals and provides positive pulses at the terminal 253, and the reference 282 indicates a transistor which amplies the negative signals and provides positive pulses at the terminal 284.

In Figure 8, which represents the signalling connection through the line 22 in the direction from the central station to the concentrator, the references appliedto similar members are the same as those in Figure 7. 'i

The identication signal translator at the central station is shown in Figure 9. It is very similar to the concentrator itself and the parts which are the same as those in Figure l are indicated in Figure 9 by reference numerals increased by 900. Thus there Will be found the control and test register 904, its generator 905 and its associated decoder 906, the subscribers register 907 and the trunk register 917 and its associated decoder 918. The subscribers register 907 can, for example, be connected to subscribers gate circuits arranged at the input leads of the central station in the same way as the subscribers register 7 (Figure 1) is connected to the gate circuits 2.

The structure of the concentrator according to the The capacitor 233 is charged to a n i12 r invention having been fully described, its operation will now be explained and described.

CASE L REMOVAL oF HANDSET BY CALLING SUBSCRIBER l I. (1).--Connecti0n of the calling subscriber throughV the concentrator The loop of the subscriber 1 being closed as a result of the removal of his handset and the subscribers line 3 being unconnected, the detector 203 detects the closing of the loop, as a result of which the and coincidence circuit 205 of the gate circuit 2 is rendered conductive. When the subscribers register 7 and the subscribers distributor 8, advancing under the control of the generator 16, arrive at the point 82 of the calling subscriber, the and not coincidence circuit 204, which is open owing to the absence of current in the resistor 202, allows the pulse arriving on the lead 182' to pass and this pulse, amplified by the marking amplifier 209, energizes and res a crosspoint 13 of the switchboard 10.

As a consequence of this crosspoint iiring, the line 3, coupled to the incoming lead 11, is connected with an outgoing lead 12 of the switchboard 10. A current passes through the resistor 202 and the coincidence circuit 204 is inhibited by way of the lead 213. The calling subscribers gate circuit is henceforth locked and becomes unsensitive to the pulses coming from the subscribers distributor 8.

The iiringof a diode 13 also causes an increase of potential at the point 234 (Figure 6) of the trunk equipment 23 corresponding to the fired diode. This increase of potential diiierentiated by the capacitor 235 and resistor 236, causes the transmission of a positive pulse over the lead 253, which pulse energises the input of the trunk coder 15 (Figure l) and sets the four trigger circuits 171-174 of the trunk register 17 which identities the connected trunk.

The trigger circuit 32 which, as already stated, is intended to mark the phase of the transmission of the identification signal to the central station which is connected to the output of the or coincidence circuit 207, is brought to its operated condition by way of the lead 211 which is connected in common to all the subscribers gate circuits 2. The said trigger circuit 32 prepares the transmission of the calling subscribers identication signal and that of the connected trunk.

1(2). Identification of the calling subscriber The trigger circuit 32 being in its operated condition, the potential of the lead 6 7 (Figure 3) and that of the points 717 (Figure 4) is reduced and, as has already been explained, the pulses from the generator 16, which are intended to control the subscribers register 7, become ineffective. The subscribers register 7 stops counting and stores the number of the calling subscriber.

At the same time the blocking potential supplied by the trigger circuit 32 in its rest condition to the generator 5 by way of the and coincidence circuit 65 is removed. 'Ihe generator 5 starts to oscillate and supplies counting pulses to the control and test register 4 which begins to seek the calling subscriber stored in the subscribers register 7.

Each of the outputs a0 to 1115 of the control and test decoder 6 receives in turn a positive pulse. The sending device 29, in the positions a0 to a6 inclusive, receives through the leads 51+ and 51- pulses which arrive from one lead or the other according to the condition of the trigger circuits 71-76 of the fsubscribers register. In the position a0, the corresponding pulse arrives at the sending device 29 through the lead 51+, as seen in Figure 3.

The sending device 29 converts the pulses which it receivesfrom the lead 51+ into positive pulses on the signalling line 20, and converts the pulseswhich it receives from the lead 51- into negative pulses on this same aeraeei The .eallius subserihers identifie, '9u

identification pulses arrive yatt-thesending `device 2 9v by Sway tQi `the and -e'oine'ideuee 'circuits 68, which are conductive during the l.'.iltern'atio'ns of operation of the ,generater The ypulseernittedby r.the ,control and test decoder on lead l35 (Figures 1 and?) in the Vposition a7 remains ineffective, because the fand noti coincidence' circuit l204 isblocledufromthe `moment when `the diodel 13 operates. It will later be seen how the calling subscribers identification signal is received bythe central station.

1(3) Identification `of ythe .connected trunk v`iiietributer ef the same kindl S tite-.Subscribete .distributor 18,1whih iS 'tself QOuueCted-to theeubseribers 4.re'sister.91151- Once the number ofthe calledsub'scriber is "stored, control Aand testregister .904 Starts.itsseanuiusgneratieu under the'control of the .generatortl )andjtheidentiiication signal of this subscriber .iS seut by the Sending In the positions a9 toalz ,the control andtest decoder tests the QQnditiqn'of .'thelrigger circuits 171-174 of the .resister '17 as it had pr'eyieuely tested the eeuditieu of the trigger circuits',571-716V of the subscribers register 7. flfhe p'iilse emitted by the control and test decoder bri-lead 36 (Figures 3 andA) in `the position am remains yineffective because the .trigger circuit 32 in its operated ,cendition maintains the lead 36 at `a low potential.

' The pulse emitted by the control andV test decoder o n leads 47 and 48 in position 115 lserves to restore the trigger circuits 1171-174 ofthe trunk register J17, as yvell as the trigger circuit3 2, to therest condition. The trigger cir- .cuit v32,b ei n g thus returned toits rest condition and the .is again raised. The subscribers register 7 again becomes ",eiective to operate asa scaler and this register again advances under the control of the generator 16,

' The identification signal .of the calling subscriber and that o f the connected ftrunk are received and utilized at the central station in the following manner.

The identification signal receiver 928 at the central station receives the Startsignal, the identification signal of the calling rsubscriber which it applies to the v'subscribers register 907 andthe identification signal ,of the connected trunk Which it applies to the trunk register 9,17. Ihepperation o f the registers 907fand 917 is completely analogousto that `of the registers 7 and I1,'7 when they' record lthe subscriber identification signal and the trunk identification signal transmittedV by the central sta- Q Which will be explained in the following Case II. l cThe identity of the calling subscriber which is given by the contents of the register 907 is stored until the instant when the called subscriber replies. This stored information is then used to effect the charging of the communication.

The identity -of the ktrunk is given by the contents of the ifegister 9 17, which is utilised, through the intermediary 'of'tthedecoder918,.to Yensure the marking of the correonding incoming trunk equipment 923, which yenables EP central 'station to connect this incoming trunk equipjrnent first topa conventional `sender andthen to the ofthe caiied subscriber.

CAsan. coNNECnoN oF THE CALLED 'r sUBscniBEn r11(1). Marking of the called subscriber-s line The Anumber of the called subscriber to be connected is `introduced into the subscribers register 907 by the central ,device 92,9 over the signalling line 22'to the receiving .device 28- AS in CaSe'I, this ideutieatieu Signal is la group 0f six ideutiiieatieu ruleeslpreeeded by fa Positive .1 0

start pulse.

The receiving .device 28 sends the positive identification pulses along the lead 31+ and the negative pulses @199g the lead 31-. The pulse repeater 38 is brought into operation .at each pulse, whatever the lead en which the said pulse appears.

AS S0011 as the Start Pulse is received, the triest-:r eircuit 33, which characterizes the phase of the identiiication signal reception of the central station is'operated through the path (Figure vv3): :lead `30, or lcoincidence vcircuit 37, puise 4repeater trigger circuit 38, fand y coincidence circuit 39,'lead 40 and trigger circuit vv33. The operation .of the latter taltes place only during the alternations `of ,operation of the generator 1 6, owing to vthe coincidence circuit 39.

The and coincidence circuit `466k connectedsto the receiver 28 yand vto the trigger circuit 33 remains closed because the start pulseis not negative.

The trigger circuit 33 being in its operated `condition,

the potential of the lead 67 (Figure 3) land that fof the points 717 (Figure 4) arereducedand in the sarne Way as Vin `Case I the pulses from the generator 16 intended for the control of the subscribers register 7, become ineffective. The subscribers register 7 `then ceases to operate as a Scaler. In addition the reduction of po-tential of the lead 34 (Figure 4) causes the unblocking of all the vvdiodes 711, 712, 721, 722 and the inhibition of all the .out-

Y puts 81%144 of the subscribers distributor-8.

v corresponding identification pulse. Contrary -to the operation in Case I the existing condition of the trigger circuits is not tested .but instead they are made to take up a predetermined condition. -For example, if the triggercircuit f 71 is in its rest condition and `if the first identification pulse is positive, the coincidence circuit 49 receives from the terminal a1 a positive pulse and, yfrom the lead 50, a positive potential. A positive pulse therefore leaves this coincidence circuit 49 and all-Pears at the input of the coincidence circuit 9 at the moment when thislatter receives a positive pulse from the lead 31+. A positive pulse therefore leaves this coincidence circuit 9 arid sets the trigger circuit 71 to its operated condition. Of course, if the trigger circuit 71 had already b eenin operated condition,

' there would have been no positive potential on the lead S0, no positive pulse at the output of the coincidence circuits 49 and 9, and the trigger circuit 71 would Ahave remained in its operated condition.

v\II(2). Connection of the called subscriber through his concentrator At the end of the sixth received identification pulse, ythe pulse repeater 38A assumes the rest condition and the control and test decode r6 passes to its position a7. The p ositive pulse which appears at the terminal a7 is applied on the Yone hand to the coincidence vcircuit 57 and on the other hand to the gate circuit 2, in bo-th cases through the lead 35 (Figure 2).

The trigger circuit 33 is returned to the rest condition through the coincidence circuit 57 and during an alternation of operation of the generator 16, and this causes the termination of the inhibition of the outputs 81-144 of the subscribers distributor 8.

The pulse coming from a7 passes through the coincidence circuit 206 of the called subscribers gate circuit, provided that the latter is not already connected. The coincidence circuit 204 is then conductive, because the subscribers distributor 8, the outputs of which are no longer inhibited, is marking the lead 182 at the moment in question. The pulse coming from the coincidence circuit 206 is amplified by the marking amplifier 209 and operates a diode 13 of the switchboard or matrix 10, thereby causing the Vconnection of the called subscriber. It brings the trigger circuit 32 to its operated condition.

II(3). Identijcaton of the selected trunk At the end of the period 11(2), the conditions of Case I are again existing, with the difference that the control and test decoder is in position a7 instead of position a0. The identification of the connected trunk is effected as in Case I. The trigger circuit 32 continues to inhibit the scaling of the subscribers register 8. In addition, in assuming its operated condition, this trigger circuit removes the blocking potential applied to the generator through the coincidence circuit 65, and the generator 5 commences to operate.

The control and test decoder advances no longer under the control of the pulses repeater 38, but under the control of the generator 5. As a result the identification signal of the connected trunk is transmitted in positions a9 to am. The pulse transmitted on lead 36 (Figure 5) in position am remains ineffective because the trigger circuit 32 is in operated condition. As in case I, the pulse transmitted in position als restores to their rest conditions the trigger circuits 171-174, trigger circuit 32, generator 5 and control and test register 4, and causes the subscribers register 7 to recommence operation as a sealer.

CASE fIII.-DISCONNECTION OF A TRUNK LINE III(1). Marking the trunk line to be disconnected The number of the trunk line to be disconnected is introduced into the trunk register 917 by the central station. has been stored, the control and test register 904 com- .mences to scan under the control of the generator 905,

but jumps its first eight positions a0 to a7. The identification signal of this trunk is transmitted by the scanning device 929 over the signalling line 22 to the receiving device 28. This identification signal is a group of four identification pulses preceded by a negative start pulse.

The receiving device 28 transmits the positive pulses over lead 31+k and the negative pulses over lead 31. As soon as a negative start pulse is received, the trigger circuit 33, which characterizes the phases of reception of identification signals from the central station, is brought to its operated condition through the same channel as in case II and the and coincidence circuit 66 becomes conductive a short period before the trigger circuit 33 is set to its operated condition. The trigger circuit 44 of the control and test register is thus set directly to its operated condition, thereby causing the test decoder to pass directly to its position a8. t

The trigger circuit `33 being in its operated condition, the pulses from generator 16 for the control of the subscribers register 7 become ineffective. The subscribers register 7 stops operating as a sealer. In addition, all the outputs 81-144 of the subscribers distributor 8 are inhibited.

Control and test register 4 advances in the manner of a sealer each time the pulse repeater 38 returns to rest condition and positive pulses appear successively at the Once the number of the trunk for disconnection.

Y '16 n terminals a to 115. As in Case II the generator 5 remains blocked during this advancement because the trigger. circuit 32 characterizing the code transmission phases is in rest condition and because a blocking potential is maintained at the generator 5 through the coincidence circuit 65.

In positions a9 to am, trigger circuits 171-"174 are brought to the condition which corresponds to the sign of the corresponding identification pulse. For example, if the trigger circuit 171 is in rest condition and if the first identification pulse is positive, the coincidence circuit 59 receives a positive pulse from the terminalrag and a positive potential by way of the lead 60. A positive pulse is therefore produced by this coincidence circuit 59 and appears at the input of the coincidence circuit 19 at the moment when this latter receives a positive pulse through the lead 31+. This coincidence circuit 19 therefore produces a positive pulse and brings the trigger circuit 171 to its operated condition. Of course, if the trigger circuit 171 had already been in operated condition there would have been no positive potential on the lead 60, no positivepulse at the outputs of the coincidence circuits 59 and 19, and the trigger circuit 171 would have remained in operated condition.

III(2). Dsconnecton of a marked trunk line At the end of the reception of fourth identification pulse, the pulse repeater 38 assumes its rest condition and the control and test decoder 6 goes to position 113. The positive pulse which appears at the terminal als (Figure 5) is effective in the present case, because the trigger circuit 32 is in rest condition. The inhibition of the trunk register 17 terminates and the positive pulse which appears at the terminal 183 is applied through the lead 283 to the trunk equipment 23 in which it causes the disconnection to be made; After passing through the transistor 238, which reverses the polarity of the pulse, the pulse is applied to the disconnection amplifier 231 which provides a positive output pulse of the required amplitude on the lead 12 of the switchboard or matrix 10, which results in the extinction of the corresponding diode 13 of the matrix.

In positions al., and i115, advancement of the control and test register 4 is again causedby generator 5. The coincidence circuit 65 stops transmitting the blocking potential for the generator 5, which is provided by the trigger circuit 33, as long as the following situation exists: trigger circuit 33 in its operated condition and all trigger circuits 42, 43, 44 in operated condition, that is to say in positions al., and 115 of Case HI.

In position 115 trigger circuits 171-174, trigger circuit 33 generator 5 and control and test register 4 are restored to rest condition and subscribers register 7 resumes its operation as a scaler.

Finally, the possibilities of extending the invention will be considered. In particular the case of a concentrator having two stages of crosspoints will be discussed.

For a concentrator having one stage of crosspoints with m subscribers and n trunks, the number of crosspoints per subscriber is n. If m and n are large, it is advantageous to use a two-stage concentrator because the number of crosspoints per subscriber can be much lower than n for a given probability of'blocking, and in addition the ratio of concentration m/n can be increased fora given blocking probability. This results in reducing the total number of Vtrunks terminating at the central station and therefore also the number of crosspoints required inside the central station.

In the case of a two-stage concentrator, in general it can no longer be assumed that the crosspoint will select itself merely by marking the subscribers side; but in accordance with the guiding principle of the independent connection concentrator, it is desirable to avoid requesting the central station to indicate before connection the trunk to be selected. Y.

the identity of the selected line by way of the trunk coder 15, it is made to advance step by step while a very small marking current is maintained through allk the available paths from the subscribers line.

At each step the trunk register 17, now operating as a distributor, notes the presence or absence on v'the trunks of a potential characterizing the fact that the small marking current is present or is not present on this trunk, and therefore that it is suitable or unsuitable for establishing apath with the marked subscribers line. As soon as a line having the small marking current is found, the advancement of the register 17 stops and a special trigger circuit 1001 in the trunk equipment 1023 is operated, and this serves to short-circuit the very high impedance which was until this time in series with the connection circuit and therefore to allow a normal current to ow through the selected path. From this moment the remainder of the operation is identical because the register 17 contains the number of the selected trunk. To disconnect the trunk, the register 17 actuates the same trigger circuit 1001 of the trunk equipment 1023 to restore it to rest condition, and this ensures the disconnection by restoring a very high impedance in the circuit.

When the marking of the line 11 is effected by the marking amplifier 209, all the diodes of the switchboards 10, 10', and all the lines 12 are loaded by the very high resistor 1002. The current flow, which is very small (for example, 50 microamperes), charges the capacitor 1003 through the diode 1004, the charging period being, for example, 100 microseconds. All the capacitors y1003 of the equipments 1023 which can be utilized to connect the trunk 11, and only these, are therefore charged. It a positive pulse of volts, for example', is applied to the output 183 of the trunk register 17, this pulse will suiiice to unblock the diode 1005 and to drive the trigger circuit 1001 to its operated condition. lf` the capacitor 1003 is charged, the potential of point 1006 is veryslightly less than that of point 1007 which is itself at 5 volts positive with respect to the negative terminal of the battery.

If on the contrary the capacitor 1003 is not charged,

the point 1006 is practically at the potential of the negative terminal of the battery and the pulse will not be suflicient to unblock the diode 1005.

When the trigger circuit 1001 is in operated condition it permits the operation of the short-circuiting transistor 1008. The nominal ow of the diodes of the switchboard 10, (for example l0 milliamperes) is then provided through the diode 1009, the resistance 1010 and transistorv1008, a circuit the impedance of which is much less than the resistance 1002.

When the trunk is to be disconnected (extinction of the diodes of switchboards 10, 10 it is only necessary to return the trigger circuit 1001 to rest condition through the output 1183 of the trunk register 17. This blocks the transistor 1008. `The diodes are then again in series with the very high resistor 1002, but, owing to the fact that there is nolonger any marking by the marking amplifier 209 on line 11, kthey cannot continue in operated condition and are extinguished.

It has been assumed that in the case of the concentrator with two stages of crosspoints, the trunk decoder 18 had two outputs 183 and 1183 per trunk equipment 1023, one pertaining to the, scanningvof the connected 'trunks or more accurately the trunks capable ofv being connected and to the selection of these trunks,and the other pertaining to the disconnection. It could also be arranged that @11119 terminalS 1183er@ all the :trunk equipment .cir-

cuits 1023 were connected in parallel to the leadf3'6 connected to the terminal als of the test decoder, the trigger circuit 1001 beingrthen driven through an and coincidence circuit similar to the coincidence circuit 206 of Figure 2 by pulses arriving simultaneously at the terminals 183 and 1183.

Although the invention has been described in detail in connection with specific examples lof electric circuits, it will be understood that numerous variations obvious to a man skilled in the art are'possible and that these variations are within the scope of the invention.

vWhat We claim is:

1.l 1n atelephone system, a central office; a plurality.

i of lines; a plurality of trunks less in number than said plurality of lines and connected to said central office; and an independent connection line concentrator for establishing connections from any one` of said lines to a random selected idle one of said trunks and comprising tirst and second auxiliary lines, subscriber gates responsive to the service condition of the subscriber lines, trunk circuits responsive to the connection condition of the trunks, a crosspoint matrix having lines and columns respectively connected torsaid subscriber gates and trunk circuits, a subscriber register means adapted both to free run for scanning said subscriber gates and to store a given subscriber identification number, a trunk register means adapted to store a given trunk identification number and a control and test register means adapted both to free run for serially applying the digits stored in said subscriber and trunk register means to said auxiliary line and to be controlled by said central office for serially applying the digits of the identification number of a called subscriber and of a trunk to be disconnected conveyed by said second auxiliary line to said subscriber and trunk register means. Y

2. In a telephone system, a central office; a plurality of lines; a plurality of trunks less in number than said plurality of lines and connected to said central office; and "an independent connection line concentrator for establishing connections from any one of said lines to a random selected idle one of said trunks and comprising in combination a rst auxiliary line adapted to convey from said concentrator to said central o ice serial code signals representative of the numbers of calling subscriber lines and of the connected trunks, a second auxiliary line adapted to convey froml said central oice to said concentrator serial code signals representative of the numbers of called subscriber lines and of the trunks to be disconnected, subscriber gates responsive to the service condition ofthe subscriber lines, trunk circuits responsive to the connection condition ofthe trunks, a crosspoint matrix having lines and columns respectively connected to said subscriber gates and trunk circuits, a subscriber register means having first terminals connected to said subscriber gates and second terminals connected both to said first and' second auxiliary lines, said subscriber register means being adapted both to free run for scanning its first terminals and to store a given number on its second terminals, a trunk register means having first terminals connected to said trunk circuits andsecond terminals connected both to said first and second auxiliary lines, said trunk register means being adapted to store a given number on its first and second terminals, and a control register means having terminals connected to said subscriber register means and trunk register `.means which is adapted both to free run forscanning its terminals and to serially apply the digits of the number stored on the second terminals of the subscriber register means and on the second terminals of the trunk register means to said first auxiliary lines and to'be controlled by said central ofiice and serially apply the digits of the number conveyed by said second auxiliary line to said v subscriber and trunk register means,

3. In a telephone system, a central office; a pluralityof lines; a plurality of -trunks less in numberV than said plurality, of lines-and connected to said central oce;

i9 and an independent connection line concentrator for establishing connections from any one of said lines to a random selected idle one of said trunks and comprising in combination a first auxiliary vline adapted to convey from said concentrator to said central otiice serial code signals representative of the numbers of calling subscriber lines and of the connected trunks, a second auxiliary line adapted to convey from said central oice to said concentrator serial code signalsrepresentative of the numbers of Vcalled subscriber lines and of the trunks to be disconnected, subscriber gates responsive to the service condition of the subscriber lines, trunk circuits responsive to the connection condition of the trunks, a crosspoint matrix having-lines and columns respectively connected to said subscriber gates and trunk circuits, a subscriber register constituted by a number of trigger circuits adapted for registering the numbers of the subscriber lines connected to said concentrator and comprising, for each trigger circuit, auxiliary gates, two test and positioning terminals connected in parallel through said auxiliary gates to said irst and second auxiliary lines and an output, a binary to decimal decoder having binary inputs and decimal outputs the inputs of which are connected to the outputs of said subscriber register and the outputs of which are connected to said subscriber gates, and a free running oscillator adapted to drive said subscriber register for scanning said subscriber gates until the subscriber register is stopped in the position corresponding to a calling subscriber line, thereby storing its number and operating its connection at random with an idle trunk, a trunk register means having rst terminals connected to said trunk circuits and second terminals connected both to said rst and second auxiliary lines, said trunk register means being adapted to store a given number on its first and second terminals, and a control register means having terminals connected to said subscriber register and trunk register means adapted both to free run for scanning its terminals and serially apply the digits of the number stored in said subscriber register and on the second terminals of the trunk register means to said rst auxiliary lines and to be controlled by said central ofiice and serially apply the digits of the number conveyed by said second auxiliary line to said subscriber register and trunk register means.

4. YIn a telephone system, a central otiice; a plurality of lines; a plurality of trunks less in number than said plurality of lines and connected to said central oice; and an independent connection line concentrator for establishing connections from any one of said lines to a random selected idle one of said trunks and comprising in combination a first auxiliary line adapted to convey from said concentrator to said central otlice serial code signals representative of the numbers of calling subscriber lines and of the connected trunks, a second auxiliary line adapted to convey from said central office to said concentrator serial code signals representative of the numbers of called subscriber lines and of the trunks to be disconnected, subscriber gates responsive to the service condition of the subscriber lines, trunk circuits responsive to the connection condition of the trunks, a crosspoint matrix having lines and columns respectively connected to said subscriber gates and trunk circuits, a subscriber register means having first terminals connected to said subscriber gates and second terminals connected both to said first and second auxiliary lines, said subscriber register means being adapted both to free run for scanning its lirst terminals and to store a given num-t ber on its second terminals, a trunk register constituted by a number of trigger circuits adapted for registeringk the numbers of the trunks connecting said concentrator to said central oiiice and comprising a resetting input and for each trigger circuit auxiliary gates, two test and positioning terminals connected in parallel through said auxiliary gates to said rst and second auxiliary lines, a positioning input and an output, a decimal to binary coder having decimal inputs kand binary outputs the inputs of which are connected to said trunk circuits and the outputs of which are connected to said positioning inputs of said trunk register, a binary to decimal decoder having a general disconnection input, binary inputs and decimal outputs, the binary inputs of which are connected to the outputs of said trunk register and the outputs of which are connected to said trunk circuits, and a control register means having terminals connected to said subcriber'register means and trunk register adapted both to free run for scanning its terminals and serially apply the digits of the number stored on the second terminals of the subscriber register means and in the trunk' register to said iirst auxiliary lines and to be controlled by said central oice and serially apply the digits of the number conveyed by said second auxiliary line to said subscriber register means and trunk register.

5. In a telephone system, a central office; a plurality of lines; a plurality of trunks less in number than said plurality of lines and connected to said central oice; and an independent connection line concentrator for establishing connections from any one of said lines to a random selected idle one of said trunks and comprising in combination a first auxiliary line adapted to convey from said concentrator to said central ofce serial code signals representative of the numbers or" calling subscriber lines and of the connected trunks, a second auxiliary line adapted to convey from said central oiiice to said concentrator serial code signals representative of the numbers of called subscriber lines and of the trunks to be disconnected, subscriber gates responsive to the service condition of the subscriber lines, trunk circuits responsive to the connection condition of the trunks, a crosspoint matrix having lines and columns respectively connected to said subscriber gates and trunk circuits, first and second auxiliary gates, a subscriber register means having irst terminals connected to said subscriber gates and second terminals connected both'through said iirstauxiliary gates to said first and second auxiliary lines, said subscriber register means being7 adapted both to free run for scanning its rst terminals and to store a given number on its second terminals, a trunk register means having iirst terminals connected to said trunk circuits and second terminals connected both through said second auxiliary gates to said first and second auxiliary lines said trunk register means being adapted to store a given number on its iirst and second terminals, a binary to decimal control decoder having binary inputs and decimal outputs, these decimal outputs being connected respectively through said first and second auxiliary lines to said second terminals of said subscriber and trunk register means, to said first terminals of said trunk register means and to said subscriber gates in parallel, and a control register having outputs connected to said binary inputs, comprising a free running oscillator and having an input connected to said second auxiliary line, said control register being adapted both to free run for scanning said decimal outputs of said control decoder, there by providing the transmission onto said first auxiliary line of the numbers of a calling subscriber line registered in said subscriber register means and of a connected trunk registered in said trunk register means and to be controlled by said central oflice through said second auxiliary line for positioning said subscriber and trunk register means respectively according to the numbers of a called subscriber line and of a given trunk to be disconnected, and for transmittingto said subscriber'gates a pulse operating the connection of a called subscriber line with an idle trunk and to said first terminals. of said trunk register means a pulse operating the disconnection of said given trunk.

Abbatia a1. sept. 23, s Abbott et al. July 7. 1959 

